Pursuant to development of vaccination against Haemophilus influenza b, we shall serve as a reference laboratory for assays of immunity to its capsular polysaccharide PRP and other surface antigens. Antibody will be assayed by radioantigen binding or an enzyme-linked anti-globulin procedure and cellular immunity by lymphocyte culture techniques. As candidate vaccines for improved immunogenicity in infants purified PRP of high molecular weight and PRP-protein complexes of low toxicity will be sought. Vaccines tested for sterility and general safety will be produced for clinical trials.